Method of forming a conduit using a wound sacrificial layer

ABSTRACT

A thin ribbon spirally wound polymer conduit and method of forming, wherein a helical reinforcing bead is interposed adjacent overlapping layers of ribbon. Further, a method of continuously forming spirally wound conduit wherein a sacrificial layer, preferably having a different base polymer to that of the conduit, is first applied to the former before the conduit is formed overtop.

BACKGROUND TO THE INVENTION

1. Field of the Invention

The present invention relates to components for breathing circuits andin particular to conduits for use in the limbs of breathing circuits.The invention also relates to methods of manufacturing such conduits.

2. Summary of the Prior Art

In assisted breathing, particularly in medical applications, gases aresupplied and returned through conduits. Such conduits are ideally lightand flexible to achieve the highest possible level of comfort for thepatient. In the prior art, thin walled conduits are known which includehelical or annular reinforcing ribs which act to give the conduit betterresistance to crushing and pinching, while still allowing the conduit tobe light and flexible. A cross section of the wall of an example of sucha conduit is shown in FIG. 1.

It is advantageous to manufacture this type of conduit as a continuousprocess. In the prior art this is achieved by the spiral winding of athin polymer tape (ribbon or film) onto a former such that the edges ofadjacent layers overlap a small amount. A bead of molten polymer is thenapplied over top the overlapping edges welding them together andsimultaneously forming the helical reinforcing ribs. A disadvantage withthis forming technique is the difficulty welding several adjacentlayers. This problem is especially severe when multiple layer conduitwalls are to be formed. While combining the application of a molten beadwith another secondary thermal welding process or applying the polymerto the former as a still molten plastic does go some way to alleviatingthis difficulty, these solutions add complexity to the tube former andmay be difficult to achieve with very thin walls.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a conduit, withparticular application to the limbs of a breathing circuit, which willat least go some way towards improving on the above or which will atleast provide the public and the medical profession with a usefulchoice, and/or to provide a method of manufacturing conduit which willat least go some way towards providing the public and manufacturers witha useful choice.

In a first aspect the invention may broadly be said to consist in amethod of continuously forming conduit comprising:

-   -   continuously applying at least one thin film ribbon, each having        “leading” and “trailing” lateral edges, spirally around a former        rotating and advancing said conduit, with the leading edge of        each turn of ribbon overlapping the trailing edge of a previous        turn of ribbon on the former and the trailing edge of each turn        under lapping the leading edge of a succeeding turn, while,    -   in advance of said overlapping of said turns, applying a bead of        molten plastic along the exposed trailing edge of the most        recently applied turn on said former, such that a said bead is        interposed between said trailing edges and said overlapping        leading edges and    -   said overlapping portion conforms to the contour of said bead,        so that said over lapping edge meets or substantially meets said        under lapping ribbon at the edge of said bead.

In a further aspect the method of continuously forming conduit mayinclude the additional step of applying one or more heating wires to theexposed trailing edge of the ribbon prior to applying the bead, suchthat the bead encapsulates the one or more heating wires onto the saidtrailing edge.

In a further aspect the invention may broadly be said to consist in amethod of continuously forming conduit wherein the former includes aplurality of rotating rods spaced about an axis and acting to supportand advance the conduit during forming, further comprising:

-   -   first applying a sacrificial layer of thin plastic around said        former, before said conduit is formed on said former over top of        said sacrificial layer, and    -   subsequent to forming said conduit, removing said sacrificial        layer from inside said thin walled conduit after cooling.

In a further aspect the invention may broadly be said to consist in aconduit formed in accordance with a method according to any one of thepreceding paragraphs.

In a still further aspect the invention may broadly be said to consistin a conduit comprising:

-   -   at least one thin plastic ribbon having a leading and a trailing        lateral edge, said ribbon arranged helically with its face        substantially parallel with the helix axis, and, apart from at        its ends, the leading edge of each turn of ribbon overlapping        the trailing edge of a previous turn, and the trailing edge of        each turn of ribbon underlapping the leading edge of a        succeeding turn,    -   a plastic reinforcing bead interposed between each overlapping        leading and trailing edge.

In a still further aspect the invention may broadly be said to consistin apparatus for continuously forming conduit comprising:

-   -   a former for receiving at least one thin plastic ribbon, said        former drawing said ribbon around and advancing said ribbon        along to procure a helical arrangement of said ribbon, the pitch        of said helical arrangement being somewhat less than the width        of said ribbon,    -   means for delivering a ribbon to said former at a first position        on said former, and    -   means for continuously delivering a molten bead to said former        at a second position less than one turn pitch from the position        of delivery of said ribbon, said second position corresponding        to an expected position of the trailing edge of a ribbon        delivered by said means for delivering a ribbon.

In still a further aspect the invention may broadly be said to consistin apparatus for continuously forming conduit comprising:

-   -   a former for receiving plastic ribbon, said former drawing said        ribbon around and advancing said ribbon along, to procure an        overlapping helical arrangement of said ribbon, the pitch of        said helical arrangement being somewhat less than the width of        said ribbon,    -   a first means for delivering a first ribbon to said former, at a        first location    -   a second means for delivering a second ribbon to said former, at        a location subsequent to said first ribbon,    -   a means for continuously delivering a molten bead to said former        at a position less than one turn pitch from the position of        delivery of said second ribbon said position corresponding to an        expected position of the trailing edge of said second ribbon.

In a further aspect the invention may broadly be said to consist in amethod for removing a releasable inner layer from within a conduitcomprising:

-   -   placing said conduit, including said inner layer around an        elongate shaft having a longitudinal slot,    -   forming an adequate seal toward a first end of said shaft,        effective for the conduit to at least substantially seal said        slot, from the surroundings, apart from at the other end of said        shaft,    -   applying suction to said slot,    -   initiating release of said inner layer from said conduit,    -   removing said conduit from said shaft after said inner layer is        released from said conduit.

In a further aspect the invention may broadly be said to consist in anapparatus for assisting removal of a releasable inner layer within aconduit comprising:

-   -   an elongate shaft having a longitudinal slot,    -   a effective sealing means for making an adequate seal between        said inner layer and said shaft, toward a first end of said        shaft,    -   a means to suck gases from said slot, and release said inner        layer from said conduit.

To those skilled in the art to which the invention relates, many changesin construction and widely differing embodiments and applications of theinvention will suggest themselves without departing from the scope ofthe invention as defined in the appended claims. The disclosures and thedescriptions herein are purely illustrative and are not intended to bein any sense limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional side elevation of a wall of a conduitaccording to an embodiment of the prior art.

FIG. 2 is a cross sectional elevation of a wall of a conduit accordingto one embodiment of the present invention.

FIG. 3 is a plan view of a conduit forming device for forming areinforced conduit according to a further embodiment of the presentinvention, such as the conduit pictured in FIG. 2.

FIG. 4 is a cross sectional elevation of a conduit wall showing a roughinner surface resulting from the tape not completely following thecontour of the molten bead.

FIG. 5 is a side elevation of a conduit according to a furtherembodiment of the present invention including outer axial reinforcingthreads.

FIG. 6 is a plan view of a conduit forming device for forming areinforced conduit according to an embodiment of the present invention,such as the conduit pictured in FIG. 5.

FIG. 7 is a cross sectional side elevation of a conduit wall accordingto a further embodiment of the present invention including a pair ofheater wires within the conduit wall.

FIG. 8 is a plan view of a conduit forming device for forming theconduit pictured in FIG. 7.

FIG. 9 a is a cross section of a tape or ribbon illustrating theassembly of a preformed tape including a pair of heater wires accordingto a further embodiment of the present invention.

FIG. 9 b is a cross section view of the pre-formed ribbon of FIG. 9 a,shown assembled.

FIG. 10 is a cross section view of a conduit wall including a pair ofheater wires formed from the pre-formed ribbon shown in FIG. 9 b.

FIG. 11 is a cross sectional elevation of a conduit wall showing adefect caused by the bead flowing between overlapping adjacent layers.

FIG. 12 is a plan view of an apparatus for removing the sacrificiallayer.

FIG. 13 is a plan view of the apparatus of FIG. 12, shown with a conduitovertop.

DETAILED DESCRIPTION

The present invention relates to breathing conduits in general and inparticular to improved methods of forming thin film (tape or ribbon)spiral wound conduits. Consequently the present invention findsapplication in breathing conduits fabricated from a variety of materialswhich may include breathable and/or non-breathable materials (breathablematerials being capable of transmitting water vapour but not liquidwater).

In assisted breathing, particularly in medical applications, gaseshaving high levels of relative humidity are supplied and returnedthrough conduits of a relatively restricted size. Build up ofcondensation on the inside wall of the conduit is a potential result ofthis high humidity. The purpose of including a breathable region orregions in the conduit wall is to allow diffusion of water vapour fromthe expiratory limb of the breathing circuit along the path thereof.This can reduce the build up of condensation within the expiratory limbby drying the humidified gases during their flow through the expiratorylimb. This furthermore reduces the humidity of the gases arriving atancillary equipment, such as filters, ventilators and the like, reducingthe risk of condensation accumulation, thereby improving theiroperation, or alleviating potential detrimental effects.

The preferred breathable material is a hydrophilic polyester formed intoa homogeneous flat film or ribbon. This material has been foundparticularly suited to thin film productions having a wall thickness ofless than approximately 50 microns, and therefore find particularsuitability in the manufacturing methods of the present invention. Itwill be appreciated that other breathable materials may also be suitablefor forming breathable conduits. Such breathable materials may bebreathable due to their composition, physical structure or a combinationthereof.

The following embodiments will be described with particular reference tobreathable thin film wall construction from materials such as thosereferred to above. It will be appreciated however, that in the followingdescribed embodiments the material used to form the conduit walls may beeither breathable or non-breathable and may also include combinations ofboth breathable and non-breathable materials. It will be alsoappreciated for the following described embodiments that the film(s)supplied to the former may be supplied either as a preformed flat ribbonwound onto a reel or may alternatively be supplied directly to theformer from an extruder. Each of these options may have associatedadvantages and disadvantages which will be discussed later. It will alsobe appreciated by those skilled in the art that the materials suppliedto the former may require a number of guides tensioners and/or rollersin order to position the materials accurately and provide the necessarytension.

As a corollary of material cost it is preferred that the conduit wall bemanufactured to have a relatively low wall thickness, so much so thatthe conduit wall membrane may be insufficiently sturdy to be selfsupporting. Spiral or helical reinforcing members are therefore providedas part of the tubular membrane to provide support. The helical orspiral supporting members (beads) are formed from polymer materials andmay be of the same material used in the wall of the conduit or any othercompatible plastics material.

Referring to FIG. 1, the lay-up arrangement of a flexible breathingconduit known in the art is shown. Referring to FIG. 2, a breathingcircuit limb wall cross section is shown with a thin film flexible wall.The thin film or ribbon is arranged in a spiral or helix such that theedge portions 45, 46 of adjacent layers overlap and form the wall of atube. Interposed the overlapping edges 45, 46 of adjacent winds ofribbon, is a bead of polymer material bonded with the overlappingportions of ribbon sealing the joint between windings and forming acontinuous tube. The seam is formed between the edge of a first layer offilm and the edge of a second, adjacent layer of film which is laid overtop of the polymer bead while the bead is molten. The overlapping layerof film because it is so thin, closely follows the contour of the beadand results in a smooth inner conduit wall. It is desirable for theribbon to be sufficiently supple at least laterally, to conform alongits overlapping portion to the contour of the bead, so that theoverlapping ribbon may meet or substantially meet the underlappingribbon at the edge of the bead.

The accompanying figures show small gaps or spaces between thereinforcing bead and the overlapping portion of ribbon. It is to beunderstood that these spaces are present for illustration purposes only,in order to differentiate the bead from the overlapping layer in thediagrams. In practice the overlapping layer conforms to the bead andbonds, without forming large gaps or bubbles.

An example of continuous forming apparatus suitable for manufacturingthe breathing tube according to a first embodiment of the presentinvention described in FIG. 2 is shown in FIG. 3. The apparatus includesa former 1 preferably of a known type including a plurality of rotatingrods arranged around a central support rod. The rods extend from and arerotated by a gearbox within a machine stock 2. At least in the tubeforming region the rotating rods follow a helical path. The pitch angleof the rods relative to the support rod controls the pitch angle of thetube being formed. An example of such a machine is a spiral pipelinemandrel available from OLMAS SRL of Italy.

Tube being formed on the former is rotated and advanced in the directionof arrow 3 by the movement of the rotating rods. The advance speed ofthe former is selected relative to the rotational speed so that thepitch of the helical laying of the strip or tape on to the former 1 is alittle less than the width of the strip so that adjacent turns narrowlyoverlap. A first extruder 4 supplies a tape or ribbon 5 of thin filmpolymer materials with a preferred width of approximately 10millimetres. It will be readily understood that variation from thispreferred ribbon width and size of overlap is possible in order toachieve reinforcing beads or conduits having varying pitches and/ordimensions. The ribbon 5 deposits on the former 1 in a helical fashionby action of the former. The pitch of the helical disposition of ribbon5 is slightly less than the width of ribbon 5 and results in preferredoverlap of approximately 2.5 millimetres. The helical deposition ofribbon 5 forms the wall 6 of the conduit.

An extruder 7 extrudes a bead 8 of molten or semi-molten polymermaterial. The molten bead 8 deposits between the overlapping portions ofadjacent winds of ribbon 5 and is sufficiently heated to weld the stripsof ribbon 5. In the preferred embodiment of the present invention thedimensions of the molten bead 8 are approximately 2.5 millimetres wideand 1.5 millimetres high. The conduit formed according to a preferredembodiment has an approximate internal diameter of 19 millimetres,although it will be appreciated that the methods of the presentinvention may be suitable for forming conduits having thin walls,irrespective of diameter of the conduit or the dimensions of thereinforcing bead.

For breathable wall conduits the thickness of the breathable film orribbon 5 must be thick enough so that the conduit does not become tooflimsy in use, but must also be thin enough so that the conduit wall issufficiently breathable. It has been found that with polyester blockcopolymers, such as those described above, a wall thickness between 15and 35 microns fulfil these requirements. The preferred wall thicknessfor breathable conduits according to the present invention isapproximately 25 microns. A wall thickness of 25 microns has been foundto provide a useful balance between breathability, flexibility andstrength. The wall thickness for providing an optimal compromise ofproperties will ultimately depend on the specific material employed. Inthis regard the materials and preferred dimensions referred to in thedescription are illustrative and are not intended to be in any waylimiting.

During the continuous manufacture of breathing conduits according to themethod described above it has been found that overheating problems mayoccur when thin film (whether breathable or not) is used in the conduitwalls. Further, the action of the helical rods rotating and advancingthe conduit, may wrinkle or even damage the thin ribbon deposited on theformer and may reduce the finish quality of the conduit. The mandreltemperature is raised by the continuing application of the molten beadwhich may also result in the thin film overheating and sticking to themandrel or rotating rods, causing the quality of the conduit wall tosuffer and/or disrupting the forming process. In order to overcome thesepotential problems it has been found that a sacrificial layer, woundonto the mandrel in an overlapping helix pattern before the applicationof the film reduces these problems and increases the quality of theconduit produced.

In order to accomplish this task the sacrificial layer of tape issignificantly more rigid compared to the conduit wall and must notpermanently stick to the mandrel or to the inside of the conduit wall.It has been found that a material such as bi-axially orientatedpolypropylene is ideally suited for the sacrificial layer. It will beappreciated that many alternative materials having a different basepolymer to that of the conduit wall may also be suitable. The preferredthickness of the polypropylene sacrificial layer is betweenapproximately 20 and 60 microns.

Referring to FIG. 3, a sacrificial layer 17 is wound from reel 16 ontothe former before the breathable extruded tape 5. The heat from theapplied molten bead may weld the overlapping layers of sacrificial layerto each other, but does not result in any significant bonding betweenthe sacrificial layer and the conduit wall. Alternatively, a secondarythermal welding process may be employed to weld the overlapping layersof sacrificial tape before the conduit is formed overtop. Thesacrificial layer may perform many additional advantageous functionssuch as those described below:

-   1. The dummy layer protects the helically arranged rotating rods on    the mandrel from being fouled by molten plastic.-   2. The sacrificial layer increases the stability of the process and    may help prevent the overlapping layers that form the conduit wall    from slipping and moving relative to each other.-   3. The sacrificial layer provides a protective barrier between sharp    edges or small protrusions on the mandrel or rotating rods, and the    film or ribbon.-   4. The sacrificial layer shields the thin film from the higher    operating temperatures of the mandrel and reduces overheating of the    film.

It will be readily appreciated by those skilled in the art that thebenefits derived from the application of a sacrificial layer onto themandrel before forming a conduit, are not limited only to materiallay-up and construction wherein the helical reinforcing bead isinterposed the overlapping layers.

The polypropylene layer can be easily removed from the inner wall of thefinished conduit product after cooling as it does not bond significantlyto the conduit. Additional means such as water cooling of the mandrelmay also be provided to reduce overheating.

A method of removing a releasable inner layer (for example thesacrificial layer 17) from within a length of conduit 37, subsequent toforming the conduit, will be described with reference to FIGS. 12 and13. A shaft 39 is provided having a substantially hollow cylindricalshape of a length longer than that of the desired conduit productlength. The shaft 39 has a longitudinal slot 40 and is cantilevered fromstock 42. The slot of shaft 39 is in fluid connection with a suction orvacuum source 38 via stock 42.

The outer diameter of the shaft is preferably smaller than that of theconduit 37. A tapered shoulder region 41 is provided at the built-in endof the shaft 39 in order to enable an effective seal to be formedbetween the inner layer and the shoulder portion when suction isapplied. Alternatively, the seal may be formed between the shaft and theoutside of the conduit. The effect is to seal (so far as necessary) atleast the inside of the releasable inner layer from the surroundings.

In use, and in order to remove the sacrificial layer 17 from the innerwall of the conduit 37,without damaging the conduit wall, the conduit(including sacrificial layer) is placed overtop the shaft as shown inFIG. 13. An end of the conduit is slid over the shoulder portion 41 ofthe shaft 39 forming an adequate seal. The other end of the conduit ispulled back in an axial direction so that the conduit is contracted asshown in region 42, exposing and separating the end portion ofsacrificial layer 17 from the conduit. Vacuum source 38 applied to theinner space of the shaft, leads to a pressure differential between theinside and the outside of the inner layer where it has separated fromthe conduit. This urges the inner layer onto the shaft, and into theslot, and the separation propagates along the length of the section ofconduit, sucking the sacrificial layer from the inner wall of theconduit 37. The portion of sacrificial layer 17 immediately oppositeslot 40 is sucked so that it protrudes into the shaft interior. It maybe necessary to initiate this release process at the exposed end (freeend of the shaft) of the sacrificial layer 17 by hand (by bringing theseparated end portion of the inner layer adjacent the slot. Helicalreinforcing bead 43 prevents the conduit itself from being drawn intoslot 40). After release of the sacrificial layer from the inner wall ofthe conduit 37, the conduit can be easily removed by sliding it off theshaft. Removal of the vacuum from the shaft allows removal of theremaining sacrificial layer more easily.

Applying the molten bead between the overlapping layers of tape insteadof over the top of the overlapping layers may improve the weld quality,as both layers of tape that are to be welded are in physical contactwith the molten bead. This lay-up may also reduce overheating problemsby lowering the temperature necessary to properly bond the molten bead.When the prior art forming method shown in FIG. 1 is employed tomanufacture conduits from very thin film or ribbon, (for example, havinga wall thickness less than approximately 50 microns), consistentlyproducing a high quality surface within the conduit has been found to beproblematic.

FIG. 4 and FIG. 11 illustrates some potential problems which may occurduring the production of conduit resulting in inferior wall smoothness.The quality of the surface finish for the inner surface of a breathingconduit is important, because rough inner surfaces may hinder gases flowand may cause more condensation to build up in the conduit. A protrudingor flapping portion 33 may result if the underlapping layer of film isnot completely bonded to the molten bead. This problem may occur if theunderlapping portion of film is too wide or positioned on the formerincorrectly. Similarly, overflow of molten bead 35, may result in aprotrusion or defect 34, if the underlapping portion 36 of theunderlapping layer does not extend far enough under the bead. Smallvoids 9 or undulations, may result between adjacent strips of ribbon ifthe film does not closely conform to the contour of the molten bead.This may occur if the thin ribbon is not sufficiently supple. For thisreason the construction technique of the present invention is especiallysuited to conduits fabricated from thin supple film. The thin film ishighly flexible and able to conform closely to the shape of the raisedrib of the applied molten bead 8 during fabrication. By lapping veryclosely on to the bead and wrapping around the bead, the thin filmmaintains a smooth inner surface on the finished conduit product. Afurther defect 44, is shown where the overlapping portion of the layeroverlaps the bead too much. The molten bead will also flow to fill voidsor undulations between the lay-up, resulting in a smooth conduit wall.It will be appreciated that the conduit wall cross section shown in FIG.2 and FIG. 11 is illustrative and not meant to be interpreted strictlyin regard to the space shown between the bead and the conduit walllayers. The application of a sacrificial layer onto the former beforethe conduit wall is formed, is especially suited to the conduit formingmethod wherein the molten bead is applied between overlapping layers.The presence of the sacrificial layer ensures that the helicallyarranged rotating rods on the former do not become fouled with moltenpolymer.

Throughout the diagrams, the helical reinforcing bead is shown as havinga substantially semi-circular cross section. It is however envisagedthat the actual cross sectional shape of the reinforcing bead may vary.For example the presence and thickness of the film which overlaps thereinforcing bead, may affect the shape of the reinforcing bead byflattening the bead, resulting in a less rounded and more square orrectangular cross section. Further, rollers may be employed to shape thebead. The semi-circular reinforcing bead shown in the accompanyingdrawings is purely illustrative and not intended to be in any waylimiting.

It has been found that breathing conduits formed according to the firstpreferred embodiment described above are extremely light, flexible andprovide good crush resistance. However conduits having very thin wallsmay have a reduced resistance to axial deformation and/or stretching.Due to the thin tape used to form the walls of the conduit, theresulting product may be prone to expansion and/or contraction along theaxis of the conduit. In use axial forces arising from patient breathingare capable of producing axial extension/contraction along the length ofthe conduit. In order to improve the axial stiffness of such breathingconduits, a further embodiment will now be described.

In a further embodiment shown in FIG. 5 a plurality of reinforcingthreads 10, running the length of the wall and spaced around theperimeter of the tube are aligned parallel to one another andsubstantially parallel to the major axis of the conduit. The threads 10are supported by the helical bead 11, with the threads spanning thespaces between turns of the helical bead. In this embodiment it is maybe desirable to choose the reinforcing threads (material, gauge, typeand number) such that the threads are sufficiently stiff to improve theconduits ability to resist buckling under the transiently reducedinternal pressures that could be expected during patient breathing.Unrestrained or excessive buckling of the threads may result inunacceptable levels of conduit axial contraction and/or extension. Theaxial threads 10 may be spun or braided fibres or drawn or extruded monofilaments or other equivalent forms. Tensile reinforcement may beprovided by braided or spun fibres while compressive and/or flexuralreinforcement may be provided by drawn or extruded mono filaments.

A method of forming the tube according to the embodiment of FIG. 5 isdescribed with reference to the apparatus shown in FIG. 6. In particularin the machine of FIG. 6 the tube 12 is formed by helically wrapping apreformed tape or strip of polymer 13 on to a rotating former 14. Thestrip 13 unrolls from reel 15. In an analogous manner to that describedpreviously for the first preferred embodiment, a sacrificial layer ofpolypropylene 17, is wound in an overlapping helix onto former 14 fromspool 16. The sacrificial layer 17, between the mandrel and the conduitbeing formed, allows the extremely thin film to be shielded from themandrel and higher operating temperatures.

Tube being formed on the former is rotated and advanced in the directionof arrow 3. The advance speed of the former is selected relative to therotational speed so that the pitch of the helical laying of the strip ortape on to the former 14, is a little less than the width of the stripso that adjacent turns narrowly overlap. An extruder 18 extrudes a bead19 of molten polymer material. The molten bead 19 deposits between theoverlapping portions of adjacent winds of tape 13 and is sufficientlymolten to weld to the strips of tape 13. The molten bead becomes thehelical reinforcement for the finished conduit.

A freely rotatable thread laying head 20 is located over the formerafter the bead extruder 18. The rotating head 20 carries a plurality ofspools 21 holding reinforcing thread. The head 20 is rotatable by anelectric motor and drive belt 22 and 23 respectively. The head 20 ispreferably rotated at a speed synchronized with the speed of effectiverotation of the product 12. Advancement of tube along the former 14draws thread 24 from the spools 21 to be laid as parallel threads 10 onthe outside of the reinforcing bead 19. Another thread 25 is drawn fromspool 26 and wound onto the former overtop of the longitudinal threads10, laid by thread laying head 20. The thread 25 is laid on the formerin a helical pattern such that the thread lies between the helical beadof molten polymer extruded from extruder 18. The purpose of thread 25 isto provide a temporary means of securing the plurality of longitudinalthreads in position in preparation for permanent fixing. A secondextruder 27 extrudes a second bead of molten polymer material 28 anddeposits it over top the plurality of reinforcing threads 10 anddirectly on top of the first reinforcing bead 19 and bonds. The secondbead of molten polymer sandwiches the plurality of longitudinal threadsbetween itself and the first reinforcing rib formed by polymer bead 19.Thread 25 however, lies between these overlapping reinforcing beads anddoes not become permanently bonded to the conduit wall, allowing it tobe removed. Thread 25, may be discarded or drawn from the former in aposition subsequent to the application of the second reinforcing bead 28and wound onto a spool for re-use.

This embodiment of the invention provides a breathing circuit limbreinforced against crushing by the helical bead and against longitudinalextension by the axial threads 10 as well as providing a breathingconduit having all the advantages of the first preferred embodiment. Thespanning threads 10 also provide an additional advantage by reducingdirect contact between the user/environment and the surface of the tube,therefore reducing the risk of punctures and damage. The threadseffectively provide an additional barrier against potential damagearound the conduit wall. It will be appreciated that the foregoingmethod of reinforcing a conduit is not limited to conduits wherein thehelical reinforcing bead is interposed between the overlapping layers.

A further breathing circuit component to which the present invention maybe applied is catheter mounts. A catheter mount connects between apatient interfacing component such as a mouth piece, nasal mask orendotracheal tube and the dual limbs of the breathing circuit.Connection with the dual limbs of the breathing circuit is generally viaa wye connector. The extreme flexibility of very thin walled tubesmanufactured according to the methods herein, makes them particularlyuseful in a catheter mount component.

It should be appreciated that with all of the forming methods describedinvolving winding of a narrow ribbon or strip to create a tube, it wouldbe possible to wind two or more ribbons or films simultaneously onto theformer so that the turns created by each ribbon are interposed by turnsof other ribbons, edges overlapping and being bonded together by aninterposed extruded helical rib. For example a pair of ribbons may belaid as a double helix. This would require a multiplication in thenumber of forming stations associated with the wound on components ofthe tube or conduit. Further it is envisaged that for methods where apreformed tape is supplied to a former, the tape may be provided as alaminate having a thin film layer and a reinforcing layer bonded to it.Where the thin film layer is a breathable layer, the reinforcing layeris also permeable and allows the passage of water vapour.

A further embodiment of the present invention is envisaged where thinwalled breathing conduits are manufactured in a similar manner asdescribed above but, where the conduit wall also preferably contains atleast one thin conductive wire. A pair of wires may be included in orderto provide a means for heating the conduit and or to carry electricalsignals to sensors or transducers. Heated conduits may reduce the buildup of condensation in the conduit and may also offer a means tomaintaining the temperature of humidified gases flowing through theconduit. Heated conduits are most often used in only the inspiratory armof a breathing circuit but can also be used in the expiratory arm.Heated wall conduits may also be components of coaxial (unilimb)circuits, or be used in single limb applications such as for CPAPtherapy. In such breathing conduits where the inspiratory arm includesheater wires, the corresponding connectors at least one end of theconduit will include an electrical connection suitable for connectionwith the humidified gases source in order to supply electrical energy tothe conduit heater wires. Referring to FIG. 7, a breathing conduit isshown including a pair of heater wires 31, embedded in the helicalreinforcing bead.

A method of forming a conduit according to this embodiment of thepresent invention including a pair of heater wires will now be describedwith reference to FIG. 8. The method is similar to the method previouslydescribed and illustrated in FIG. 3, but an additional stage is requiredto lay a pair of parallel wires in between the overlapping adjacentwinds of film in the edge area of the film that will become the seam. Apair of wires 31 are supplied from two reels 29 and 30. The wires arelaid on top of the first wind of film, towards the edge, after it islaid on the former but before the molten bead is applied. FIG. 8 shows apair of heater wires 31 in hidden detail under the molten bead 8. Themolten bead 8 is then laid over the wires on top of the first layer offilm before the following overlapping wind of film wraps around theformer and completes the tube. It will be appreciated that each of thefilm, heating wire(s), and reinforcing bead may be applied in adifferent plane in order to achieve the desired spatial lay-up.

The resulting conduit is shown in FIG. 7 and is similar to the previousembodiment shown in FIG. 2, but includes an additional pair of heaterwires embedded in the helical reinforcing bead of the conduit wall. Inthis embodiment, a sacrificial layer 17 may also be wound in anoverlapping helix onto the former from spool 16. The sacrificial layer17 may be a polypropylene layer or some other material that will notweld to the conduit wall. The sacrificial layer 17 between the mandreland the conduit being formed, allows the extremely thin film to beshielded from the higher operating temperature of the mandrel andalleviates overheating of the film.

A further method of forming a conduit according to the present inventionincluding a pair of heater wires will now be described.

The above method of forming a conduit discloses an online process forwinding a pair of heater wires into the conduit wall. It is envisagedthat a pair of heater wires may be included in a preformed tape whichwould then be used to form the walls of the conduit in a similar methodto that described above and illustrated in FIG. 3. FIGS. 9 a and 9 bshow cross sections of such a tape being formed by laying a pair ofparallel wires a distance x from one edge of the tape. The length x oftape between the wires and the edge is then folded over and back ontothe rest of the tape so as to enclose the pair of parallel wires, asshown by arrow 32. A secondary thermal welding process may then beemployed to bond the folded portion of tape so as to permanently embedthe parallel wires. It will be appreciated however that a secondarythermal welding process may not be necessary if the extruded tape ismolten or semi-molten when the folding occurs. In this case the tworegions of molten layer, when folded and pressed together will bond.

Such a pre-formed folded tape including embedded wires may then be woundon to reels and supplied to a conduit forming process such as thatdescribed previously and illustrated in FIG. 3 to produce a breathingconduit with a pair of integral heating wires. FIG. 10 shows the lay-upof a breathing conduit formed by this embodiment of the presentinvention. The portion of thin film that wraps over the reinforcing beadand the adjacent wind on the former is only one layer thick andtherefore is able to conform to the contour of the reinforcing bead. Atube formed according to this embodiment of the present inventiontherefore is able to retain all of the advantages of the previouslydescribed preferred embodiments, while having the additional advantagethat a forming apparatus as described in FIG. 3 may be employed tomanufacture a conduit including embedded heater wires withoutsubstantial modification to the forming apparatus. In such a case theextruder 4 is replaced with a reel of pre-formed folded tape such asthat shown in FIG. 9 b and supplied to the forming apparatus.

1. A method for continuously manufacturing conduit comprising: applying a sacrificial layer of thin plastic around a former in an overlapping pattern, said former rotating and advancing said conduit, forming a conduit on said former overtop said sacrificial layer, welding said overlapping layers to each other, and removing said sacrificial layer from inside said conduit.
 2. A method for manufacturing conduit as claimed in claim 1, wherein said sacrificial layer is a thin ribbon having “leading” and “trailing” lateral edges, and said ribbon is spirally wound around said former in a continuous fashion, with the leading edge of each turn of ribbon overlapping the trailing edge of a previous turn of ribbon on the former and the trailing edge of each turn under lapping the leading edge of a succeeding turn.
 3. A method for manufacturing a conduit as claim 1, wherein said sacrificial layer is of a material having a different base polymer than that of said conduit, such that no substantial adhesion occurs when adjacent layers of said sacrificial layer and said conduit are heated.
 4. A method of continuously forming conduit as claimed in claim 1, wherein said conduit has a wall thickness of less than 400 microns.
 5. A method of continuously manufacturing conduit as claimed in claim 1, wherein the wall of said conduit is formed from a thin polymer tape having “leading” and “trailing” lateral edges, and said tape is spirally wound around said former in a continuous fashion, with the leading edge of each turn of tape overlapping the trailing edge of a previous turn of tape on said former and the trailing edge of each turn of said tape under lapping the leading edge of a succeeding turn of tape.
 6. A method of continuously manufacturing conduit as claimed in claim 5, further comprising the step of: applying a bead of molten plastic over top, or between, said overlapping turns of tape and said bead welding said spirally wound tape to form said conduit.
 7. A method of continuously manufacturing conduit as claimed in claim 6, wherein said step of applying said molten bead over top, or between, said overlapping layers of tape, welds said overlapping leading and trailing edges of said sacrificial layer of spirally wound ribbon. 